Comparison of imposer and intersex development in four prosobranch species for TBT monitoring of a southern European estuarine system (Ria de Aveiro, NW Portugal)

The prosobranchs Nucella lapillus, Nassarius reficulatus, Hydrobia ulvae and Littorina littorea were sampled from May to July 1998 at 45 stations in the Ria de Aveiro (NW Portugal) and the adjacent coastal zone. The distribution patterns of these populations were related to the salinity gradients. The tributyltin (TBT) concentration in the water was determined for 17 stations spread over the study area during a neap tide in July 1998 and varied from 9 to 42 ng Sn l(-1). The TBT contamination of unsieved sediments taken from 20 sites inside the Ria de Aveiro in July 1998 ranged from <6 to 88 ng Sn g(-1) dry weight. All populations of the 4 species showed imposer (superimposition of male characters on females) or the related phenomenon intersex, except for N. reticulatus at some inshore stations outside the ria. The vas deferens sequence index (VDSI) of N. reticulatus, H. ulvae and N. lapillus varied from 0.0-4.8, 0.2-1.1 and 4.0-4.4, respectively. The intersex index (IST) for L. littorea ranged from 0.3 to 0.5. Sterilization of females was found in N. lapillus at 1 site (29 %). This muricid was the most sensitive species to TBT, followed, in decreasing order, by N. reticulatus, H. ulvae and L. littorea. The nassariid N. reticulatus provided the best discrimination between stations with different TBT environmental contamination. his proposed that N. reticulatus and H. ulvae may jointly be used for monitoring sediments of moderately to highly contaminated estuarine systems due to their complementary distributions with regard to salinity, their common type of substrate and their ubiquity on the European coast.